Electrical-discharge device



.Aug. 20, 1929. KINGDQN 7 1,725,281

ELECTRI CAL, DISCHARGE DEVICE Original Filed Feb. 26, 1923 Ihventor:Kenneth H.Kingdon, b9 flunk Patented Aug. 20, 1929. I

um'rao STATTES PATE NT OFFICE.

KENNETH TH. KINGDON, 0] SCHENECTADY, NEW YORK, ASSIGNOR T0 GENERA LELECTRIC COMPANY, A CORPORATION OF NEW YORK.

mECTRIOAL-DISCHARGE DEVICE.

Application fled February 26, 1928, Serial No. 621,149. Renewed May 26,1928.v

The present invention comprises a new electrical discharge device. It isthe particular object of my invention to improve the operatingcharacteristics of discharge devices such, for example, as rectifierscontaining a cathode adapted to form or generate during operation asurface film of high electron emissivity, as for example, a film ofthorium as described in Langmuir Patents 1,244,216 and 1,244,217.

Prior to my invention, devices of this character have been provided witha filling of. rare gas or alkali metal vapor to improve theircurrent-can ing capacity by the reduction of space c arge. It has beenfound that when the gaseous pressure is maintained within certainlimits, say, within the range of about a few microns to a fewmillimeters of mercury, and the voltage drop at the cathode ismaintained below a value which depends on the particular gas or vaporemployed, that the film of thorium then remains intact but that athigher gas pressures or at higher voltage drop at the cathode the activeelectron-emitting film on the cathode is removed bycathodic sputtering,or positive ion bombardment. For example, when using as the ionizablemedium argon gas at a pressure of about 100 microns, in a devicecontaining a cathode of the thoriated type, (that is, containingthorium, or its equivalent), the critical voltage below which sputtering.does not occur'is about 20 to 25 volts. Claims generic to the presentinvention have been made in an application of Albert \V. Hull, SerialNo. 226,276, filed October 15, 1927, (as a continuation in part of anapplication Serial No. 594,370, filed October 13, 1922) on a device andthe method of its operation wherein a cathode, which is coated with amaterial having higher electron emissivity than the main body of thecathode, is operated in the presence of a gas while being protected fromthe destructive effect of posi tive ion bombardment. The presentapplication is an improvement of the device covered by the Hullapplication, which is assigned to the same assignee as the presentapplication.

I have discovered that when hydrogen is used as the ionizable medium, avoltage drop of as high as 125 volts between the cathode and the anodemay be used without effect invention maybe embodied. The drawing shows adevice adapted particularly for the rectification of alternating currentalthough capable of other uses. It comprises an envelope 1 in which isprovided a cathode 2 and an anode 3. The figure shows a cylindricalenvelope containing a cylindrical anode having closed ends except forperforations through which passes a linear filamentary cathode which isaxially located wlthln the anode, the filament preferably beingconnected to the supporting conductors ust outside of the ends of .theanode. I wish it to be understood, however, that my mvention is notlimited in its usefulness to the structural features shown in thisparticular embodiment. The cathode supply conductors 4, 5 are sealedinto the envelope in the usual way and intermediate between theconductor 5 and the cathode 2 is provlded a spring support 6 to maintainthe filament taut during operation. The anode 3 is supported by coiledresilient wires 7, 7 resting on the container and is connected to asealed-in conductor 8.

The cathode may consist of tungsten containing an admixture of about 4%thoria. A reducing agent, such for exampleas metallic magnesiumpreferably also is provided in the bulbs as indicated at 9.

The envelope is given the customary bakeout and high vacuum exhaust andis then filled with dry, pure hydrogen at a pressure preferably of about100 microns. The pressure may be varied according to circumstances froma few microns to a few millimeters of mercury. In order to avoid adiminution of the gas pressure within the device during operation by thephenomenon known as electrical clean-up whereby gas apparently isadsorbed by the envelope, the device is preferably aged while stillconnected to the source of hydrogen. It is sealed off when the pressureremains constant during operation. In some cases I may also provide, asshown in the drawing, a palladium valve for the admission of hydrogen.As indicated, this device may consist of a palladium tube 10 sealed intoa glass side tube 11 and closed at its outer end. The.

open end ofthe palladium tube which communicates with the interior ofthe tube is free to supply gas to the envelope through I the tube 11.When the tube 10 is heated in a flame containing hydrogen, as for e'X-ample an ordinary gas flame or Bunsen burner, some of the hydrogen isdiffused through the walls of the palladium tube into the interior ofthe device 1. v

The drawing shows my. device used as a rectifier connected by theconductors 12, 13 toa source of alternating current as represented bythe secondary of a transformer A load 15 in circuit with the rectifier14. is supplied with unidirectional current. The cathode 2 is heatedduring operation from a suitable source, not shown. When the switch 16is closed current flows through the rectifier provided that the voltagedrop between the cathode 2 and the anode 3 does not exceed the criticalvoltage of about 125 volts. If for any reason this critical voltage isexceeded, for example, due to a short circuit on the load, then thecathode loses its high electron emissivity by the removal of theadsorbed thorium film by positive ionization bombardment. The filamentcan be restored by opening a switch 16, or in some cases it may bedesirable to expedite the formation of the film of thorium by raisingthe cathode temperature to about 2100 K. for a short time.

lVhat I claim as new and desire to secure by Letters Patent of theUnited States, is

1. An electric discharge device 'comprising electrodes, including athermionic thoriated cathode, an enclosing envelope and a filling ofhydrogen therein at a pressure high enough to reduce space charge bypositive ionization.

2. An electric discharge device comprising a container, a cathodetherein capable of forming during operation a surface layer of thorium,an anode and a filling of hydrogen in said container at a pressure highenough to reduce space charge by positive ionization.

3. An electric discharge device comprising a container, a cathodetherein consisting of tungsten containing several per cent of thoria, ananode and afilling of hydrogen in said container at a pressure withinthe limits of about several'microns to several millimeters of mercury.

4. An electric discharge device comprising a container, electrodestherein, the oathode being adapted to operate at incandescence, meansfor generating a layer on the surface of said cathode capable of higherelectron emission than the main constituent of said cathode, said layerbeing sensitive to positive ionization, and a filling of hydrogen insaid container.

5. An electric discharge device comprising a sealed container electrodestherein, the cathode being adapted to form a surface layer of highelectron emissivity, a filling of hydrogen at appreciable pressure, andmeans for supplying hydrogen to said container durin the operation ofsaid device.

6. K rectifier comprising a cathode adapted to be heated toincandescence during operation, an anode, means for generating upon thesurface of said cathode a film of thorium material having a highelectron emissivity an enclosing envelope and a filling of hydrogen at apressure of about 101) microns.

In witness whereof, I have hereunto set my hand this 23rd day ofFebruary, 1923.

' KENNETH H. KINGDON.

